Specific tokens in e-mail sender name cause mails to not be received

[rudivanhierden]

Description
When the 'Email sender name for outgoing mails' contains either a ':' or a '!' (other tokens might be included as well), any email sent from this site will not be received.

Suggested fix
There needs to be an investigation into whether or not the list of ':' and '!' is exhaustive, or whether there are more tokens which may cause this issue. Once we have a complete list of tokens we can add a validation to the 'Email sender name for outgoing mails'-field to make sure these tokens can not be entered into the configuration.

Related ticket: https://trello.com/c/0aIspxZc/92-validatie-voor-email-sender-name-for-outgoing-mails-toevoegen-aan-admin-panel